1. Field of the Invention
The present invention relates to a displacement sensor using giant magnetoresistive (hereinafter referred to as GMR) elements to detect a displacement of a physical quantity such as, for example, a displacement of an angle, a gradient, or a stroke. In particular, the present invention is concerned with such a displacement sensor having means for correcting a waveform distortion of an output voltage. The present invention is also concerned with a semiconductor device used for such a sensor.
2. Description of the Related Art
Such a displacement sensor using GMR elements and a semiconductor device used for the sensor are known from, for example, JP-A-2003-121197, JP-A-2005-24287 and JP-A-2006-170837.
The GMR elements are each provided with a first magnetic layer (also called a reference magnetic layer, a fixed magnetic layer, or a pin magnetic layer) whose magnetization direction is set in a specific direction and whose magnetized state (e.g., magnetization direction or magnetization intensity in a rotational direction or in a vertical direction) is not influenced by a displacement (e.g., rotational displacement, slant displacement, or stroke displacement) of an external magnetic field and a second magnetic field (also called a detection-side magnetic layer or a free magnetic layer) whose magnetized state changes with a change of an external magnetic field.
When a relative position (a relative position in a rotational direction, a relative position in a slant direction, or a relative position in an axial direction) between an external magnetic field generator and the GMR element changes, the magnetized state of the second magnetic layer (also called a detection-side magnetic layer or a free magnetic layer) also changes, and there occurs a displacement difference in magnetized state (e.g., rotational angle, slant angle, or magnetization intensity) between the second magnetic layer and the first magnetic layer (also called a reference magnetic layer, a fixed magnetic layer, or a pin magnetic layer) whose magnetized state does not change.
The displacement difference in magnetized state between the first and second magnetic layers appears as a change in resistance value of the GMR element. A bias current is supplied to the GMR element and the change in resistance value of the GMR element is detected as a change in output voltage.
As a result, this change in detected voltage represents a displacement difference in magnetized state between the first and second magnetic layers, which indicates a displacement (e.g., a displacement in a rotational direction, a displacement in a slant direction, or a displacement of a stroke) in a relative position between the external magnetic field generator and the GMR element.